Respirators often use filter cartridges to protect a user from potentially hazardous vapors. When the respirator is in place on the user (typically attached to the face or head in a way to form a seal), air is drawn into the respirator through the filter cartridge whenever the user breathes (and air can typically only enter the respirator through the cartridge, so that the air may be filtered by the cartridge to ensure that air breathed in by the user while wearing the respirator is clean and safe). Such filter cartridges typically contain filtering material that can lock up one or more potentially hazardous vapors. As the filtering material is exposed to the vapor, it typically absorbs the vapor molecules through the pore structure of the material. Thus, by their very nature, the filter cartridges have a limited effective lifespan (after which the filtering material has absorbed all it can, and the cartridge cannot filter additional vapor). Once a filter cartridge has reached the end of its service life, it is no longer effective at protecting the user. Then the user should either remove themselves from the environment with hazardous vapors or else replace the filter cartridge on the respirator with a new cartridge. Thus, to effectively protect the user, it can be important to know when to change filters based on the service life of the cartridge.
Organic vapors are one type of potentially hazardous vapor that a respirator might filter; unfortunately, there is currently no commercially available end of service life indicator (ESLI) for organic vapors. Rather, the end of service life is often estimated based on (1) a schedule provided by the manufacturer or (2) the user actually smelling the odor of organic vapor as it penetrates an expired filter cartridge. Both of these approaches are problematic, however, since the schedule is a laboratory estimate and does not take into account the actual conditions experienced by the filter material (which could greatly impact the service life) and since the user would be actually exposed to potentially hazardous organic vapors before being able to smell odor.
Applicants have developed an end of service life indicator (ESLI) for organic vapors, so that an effective estimate of the end of service life for a particular cartridge experiencing a particular organic vapor environment can be determined. This may allow users to effectively replace filters in a safer way (reducing the risk of unintended exposure to potentially hazardous organic vapors).